1. Field of the Invention
The present invention relates to a multiprocessor type computer system having a plurality of CPUs.
2. Description of the Related Art
Recent years have seen remarkable improvement in the performance of compact computers such as personal computers and workstations. Such small computers are beginning to adopt a multiprocessor configuration using a plurality of CPUs as well as a signal processor configuration using one CPU. It is taken for granted that the performance of a computer with a signal processor configuration will reach the top soon, and a scheme of improving performance by process migration will be the mainstream.
In using a multiprocessor configuration, an increase in power consumption is inevitable. This is a big problem for a portable personal computer which needs to operate on a battery.
In a portable computer typified by a notebook personal computer, the battery operation time is an important point. It is also important for this type of computer to have a high throughput. That is, even a notebook computer needs to have the same performance as that of a general desktop computer. There has been a tendency in desktop computers toward multiprocessor configurations. This tendency is expected to accelerate.
In the field of notebook personal computers as well, therefore, in order to eliminate the difference in performance from desktop computers, the future trend would be the utilization of multiprocessor configurations. In this case, a problem is posed in terms of an increase in power consumption in the CPU section. When a plurality of CPUs simultaneously operate, the CPU section consumes power equivalent to a multiple of the number of CPUs in operation according to a simple calculation. This increase in power consumption shortens the battery operation time, adversely affecting the continuous operation time of a portable computer which is the most important point for the portable computer.
In a computer with a single-processor configuration, the power consumption of the CPU section accounts for a considerable percentage of the total power consumption of the system. It is, therefore, very important to decrease the power consumption of the CPU section. As described above, the use of a multiprocessor configuration is very effective in improving the performance of a computer, but it increases the power consumption. This makes it difficult to use a multiprocessor configuration for a portable compact computer.